The invention relates to a device for extracting gas from a microfluidics system, and, in particular, to removing dissolved air from the ink flowing into the print head of an inkjet printer.
The print head of an inkjet printer forms part of a print cartridge mounted in a carriage. The carriage moves the print cartridge back and forth across the paper. The print head includes many orifices, typically arranged in line aligned parallel to the direction in which the paper is moved through the printer and perpendicular to the direction of motion of the print head. Each orifice constitutes the outlet of a firing chamber in which is located a firing element such as a heating element or piezoelectric element. The firing element operates in response to an electrical signal to cause minute droplets of ink to be ejected from the orifice.
Ink from a reservoir is supplied to the firing chambers through an ink manifold in the print head. The ink reservoir may be located in the ink cartridge behind the print head. Alternatively, the ink reservoir may be independent of the print cartridge and be mounted in a static location. In this case, the ink flows through a flexible tube from the ink reservoir to the print head.
During manufacture, ink with a carefully controlled concentration of dissolved air is sealed in the ink reservoir. When some types of ink reservoir are installed in a printer, either independently or as part of the ink cartridge, the seal is broken to admit ambient air to the ink reservoir. This is necessary to enable air to replace the ink drawn from the ink reservoir during printing. Exposing of the ink in the ink reservoir to the ambient air causes the amount of air dissolved in the ink to increase over time.
When additional air becomes dissolved in the ink stored in the ink reservoir, this air is released from solution by the action of the firing mechanism in the firing chamber of the print head. The excess air accumulates as bubbles in the firing chamber. The bubbles can migrate from the firing chamber to other locations in the print head where they can block the flow of ink. Moreover, the additional air can be released from solution by environmental changes, such as temperature changes or changes of atmospheric pressure. The additional air can then form bubbles that can block the flow of ink in or to the print head.
It is undesirable to allow air bubbles to remain in the print head. Air bubbles can degrade the print quality, can cause a partially-full print cartridge to appear empty, requiring premature replacement of the ink cartridge. Air bubbles can also cause ink to leak from the orifices when the printer is not printing, especially when environmental changes occur.
What is needed, therefore, is a gas extraction device for use in a microfluidics system. Such a device should at least be capable of extracting bubbles of gas from locations in the microfluidics system where bubbles of gas accumulate and of delivering the gas to the atmosphere against any pressure difference that may exist. Optionally, the device should also be capable of releasing dissolved gas from the liquid in the microfluidics system prior to extracting the gas. In particular, what is needed is a gas extraction device for an ink jet printer. The gas extraction device should at least be capable of extracting bubbles of additional air from locations in the ink storage and delivery system of the ink jet printer where bubbles of air released from the ink accumulate, and of delivering the additional air to the atmosphere against the negative pressure difference that generally exists between the ink storage and delivery system and the atmosphere. Optionally, the gas extraction device should also be capable of releasing the dissolved air from the ink as the ink flows through the ink delivery system in or to the print head, or from the ink stored in the ink storage reservoir. What is also needed is a gas extraction device capable of extracting gas from a microfluidics system, and that lacks moving parts, is easy and cheap to fabricate, and that has low energy consumption. Finally, what is needed is a gas extraction device for an ink jet printer that can easily be structurally integrated with other parts of the print head, and that can be fabricated using the same manufacturing processes as other parts of the print head.
The invention provides a thermally-activated gas extraction device that comprises a bubble capture chamber, an exhaust manifold, a tapered extraction chamber and an extraction heater associated with the tapered extraction chamber. The tapered extraction chamber extends from the bubble capture chamber towards the exhaust manifold and has a cross-sectional area that increases towards the exhaust manifold.
The invention also provides a thermally-activated gas extraction device that comprises a substrate, an exhaust manifold, a barrier layer supported by the substrate, and extraction heaters supported by the substrate. Elements are formed in the barrier layer. The elements include a bubble capture chamber, a tapered primary extraction chamber and a tapered secondary extraction chamber. The primary extraction chamber extends from the bubble capture chamber, includes a wide end remote from the bubble capture chamber and has a cross-sectional area that increases towards the exhaust manifold. The secondary extraction chamber extends from the wide end of the primary extraction chamber towards the exhaust manifold, and also has a cross-sectional area that increases towards the exhaust manifold. Ones of the extraction heaters are associated with each of the primary extraction chamber and the secondary extraction chamber.
The invention further provides a first method of removing gas from a liquid. In the method, a bubble capture chamber, an exhaust manifold, and a tapered extraction chamber are provided. The tapered extraction manifold extends from the bubble capture chamber towards the exhaust manifold, and includes walls that taper outwards with increasing distance from the bubble capture chamber. A bubble of gas is accumulated in the bubble capture chamber. A portion of the liquid in the tapered extraction chamber heated to nucleate a bubble of vapor. The bubble of vapor is heated to explosively expand the bubble of vapor into contact with the walls of the tapered extraction chamber and into contact with the bubble of gas to form a composite bubble. Contact with the walls of the tapered extraction moves the composite bubble towards the exhaust manifold. Finally, heating of the composite bubble is discontinued to condense the vapor in the composite bubble.
Finally, the invention provides a second method of removing gas from a liquid. In the method, an exhaust manifold and a tapered extraction chamber are provided. The bubble capture chamber includes a boundary having a spatial energy potential. The tapered extraction chamber extends from the bubble capture chamber towards the exhaust manifold, and includes walls and a mouth. The walls taper outwards with increasing distance from the bubble capture chamber. The mouth adjoins the bubble capture chamber and is dimensioned to have a spatial energy potential less than the spatial energy potential of the boundary of the bubble capture chamber. A bubble of gas is accumulated in the bubble capture chamber. The bubble of gas in the bubble capture chamber is heated to expand the bubble into the tapered extraction chamber. After expansion, the bubble includes a first surface having a first radius of curvature in the bubble capture chamber and a second surface having a second radius of curvature in contact with the walls of the tapered extraction chamber. Heating is continued at least until the bubble of gas expands to a size at which the second radius of curvature becomes greater than the first radius of curvature and a resulting pressure difference moves at least part of the bubble from the bubble capture chamber to the tapered extraction chamber.